For decades, scientists have known that geographical genetic diversity exists. People around the world share genetic traits with their neighbors that distinguish them from peoples living further away.
Traditional anthropology has classified four races corresponding to four major continents: African, European, Asian and American. This simple system of classification dates back to the 18th century taxonomist Carolus Linnaeus and is still commonly used when describing ethnic groups and individuals. Certain areas of each continent are traditionally designated as pure representatives of each race, and other regions are assumed to be mixed between these presumably unmixed areas.
Early applications of genetic science used the traditional racial scheme in a “hand-me-down” fashion. The genetic differences between peoples traditionally identified as Black, White, Asian and American Indian in North America are great enough to allow a rough estimate of an individual's “percentage” membership in each racial group. This approach has been used for medical and police applications as well as for individuals interested in learning more about their genetic ancestry. However, this racial scheme creates problems when used outside of the core regions ancestral to modern North Americans. Mankind cannot be described by a handful of 3-5 simplistic racial categories. Simplistic divisions of the world into 3-5 continents ignores important unique regions that do not neatly fall into presumed racial categories, such as North Africa, Polynesia or India.
For instance, a Pakistani or Samoan can be classified as some percentage of American Indian, European, East Asian and Sub-Saharan Africa, but the resulting classification would be meaningless. At a theoretical level, this approach adds nothing to the popular or scientific understanding of human relationships and bestows an air of scientific legitimacy to outdated ideas of race. At a practical level, these theoretical limitations might have harmful consequences for example, for an individual administered a drug regimen based on a misleading percentage calculation. Clearly, the four-fold racial division provides an incomplete and misleading portrayal of the diversity of the human species.
Other genetic tests to determine ancestry include Y chromosome and mtDNA tests. However, while each person has thousands of ancestors, Y chromosome or mtDNA tests can only provide information about one lineage a person has inherited from one direct lineal ancestor.